import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param lists ListNode类ArrayList 
     * @return ListNode类
     */
    public ListNode mergeKLists (ArrayList<ListNode> lists) {
        // write code here
        if(lists==null||lists.size()==0){
            return null;
        }
        return mergeRangeList(lists,0,lists.size()-1);

    }
    public ListNode mergeRangeList(ArrayList<ListNode> lists,int start,int end){
        if(start>=end){
            return lists.get(start);

        }
        int mid=start+(end-start)/2;
        ListNode left=mergeRangeList(lists,start,mid);
        ListNode right=mergeRangeList(lists,mid+1,end);
        return merge(left,right);
    }
    public ListNode merge(ListNode pHead1,ListNode pHead2){
        if(pHead1==null||pHead2==null){
            return pHead1!=null?pHead1:pHead2;
        }
        if(pHead1.val<=pHead2.val){
            pHead1.next=merge(pHead1.next,pHead2);
            return pHead1;
        }else{
            pHead2.next=merge(pHead2.next,pHead1);
            return pHead2;
        }
    }
}